Space Agency

Space Agency is a rocket building/flying game. It consists of 11 training, and 30 career missions, a quick play mode and a sandbox mode, in which you have an unlimited budget and access to all of the parts that you have unlocked. It's available on the Google Play Store and Apple App Store. Also, it has been downloaded by 1 to 5 million Google Play accounts which gives away the fact that it is hugely popular.